This invention generally relates to a method and apparatus for reverse engineering an object, and more particularly, to a method and apparatus for non-destructive reproduction of an object in computer memory and associated displays as well as in a hard copy form, such as paper.
The concept and advantages of reverse engineering (RE) are not new to the industrial design and manufacturing arena but the widespread application of reverse engineering has not been seen. The simplest definition of reverse engineering is probably the designing a product from its physical model, whereas rapid prototyping (RP) builds solid models directly from computer aided design (CAD) files.
There are several methods available to reverse engineer solid physical objects to create three-dimensional images in an electronic domain. Most of these methods involve some kind of data acquisition from the surface of the object via contact or non-contact means. Though most of these methods are non-destructive in nature, some of them are destructive. The result of these methods is a computer generated image of the solid object which then can be displayed either by way of a electronic display, or in hard copy form such as paper.
Presently, some of the applications of RE are limited to redesigning old products by the same company, or for products that are in use but whose vendor is no longer in business. Effective utilization of RE, however, could save significant time and money in many other areas of business such as manufacturing.
Commercial RE processes can also be distinguished based on the various data acquisition techniques utilized by the RE system. Most of the current RE systems use one or more of the following technologies to obtain three-dimensional data from a part: (a) surface contact based technology, (b) optics based technology, (c) laser scanning based technology, and (d) radiation/x-ray/ultrasound based technology.
Of these technologies, the surface contact based technology is probably the most common. Most devices that use the surface contact technology are called coordinate measuring machines or CMM. Machines of this type employ rotary and linear encoders along with the appropriate transformation matrices in order to calculate the X, Y and Z positions of the probe tip. These coordinate triplets are then stored in a file, which can then be used to reverse engineer the surface of a part. This method is usually slow, costly, and requires a degree of skill. Moreover, if there is some critical geometry where the tip can not reach, this technique will not be able to reverse engineer that part. Most often, CMM techniques are used to perform part quality inspection and reverse engineering of simple shaped parts.
Commercial reverse engineering systems using optics have become more popular due to the increased availability of powerful computers. There are various techniques that can be used to determine a part""s three-dimensional coordinates optically. Moire interferometry, triangulation (stereo optics), and perspective reconstruction are some of them. Using the interferometry method, known patterns are projected onto the object and then read by a scanner or camera from a different known location. The fringe patterns are compared to give relative depth between areas on the surface of the part. The use of stereo optics can also provide three-dimensional data by triangulation. In this method, two scanners, such as cameras, are placed at a known distance from each other while the part is placed in between. Using a triangulation method, the coordinates of a desired location or the part can be determined. The optical method, however, has limitations based on the geometry and optical characteristics of the part. Generally the part must be rotated to capture all sides, and geometries that are hidden from the direct line of site of the imaging system cannot be scanned. Additionally, the imaging system may incorrectly interpret a part based on its optical characteristics. For example, if the surface of the part is transparent, such as a glass object, several errors may result.
A destructive optical method described in U.S. Pat. No. 5,621,648 and 5,880,961 is incorporated herein by reference. The method disclosed in these patents consists of cutting away a slice of the object, scanning the slice, and repeating this process until the object has been completely sliced and imaged. Once the object has been completely sliced the resulting images are reconstructed into a three-dimensional model. While accurate, this method is destructive and can be time consuming due to machining. Moreover, the process is difficult to use with brittle materials such as ceramics and glasses.
Laser scanning is another approach for various commercial reverse engineering systems where the lasers are primarily used for range-finding. These lasers work by scanning the part from all sides by either rotating the part or the laser. The resulting files are the same as those obtained with the contact method but can be more uniform due to automatic computer controlled scanning. These methods will not work for parts that have internal features or hidden geometry, and are inaccurate for clear or transparent parts because the laser does not reflect normally off a transparent object such as glass. Furthermore, laser scanners are generally expensive.
There also exist methods and apparatus for capturing both internal and external features of a physical object using ultrasound and x-rays. Among the methods most commonly used in a non-destructive manner include ultrasound imaging and computed tomography (CT). Ultrasound imaging is generally not an accurate means for reproducing physical measurements. CT is quite popular in the medical field and can produce accurate images. However, the machines to perform CT are quite expensive and CT presents radiation hazards because of the x-ray producing equipment that is required for this process. Some of these known methods also require substantial time investments in terms of human time as well as central processing unit time or computer time.
With the increased reliance on graphical digital models, there is a need to develop low cost reverse engineering systems that provide accurate data to industrial, entertainment, consumer, and other markets. Some of the applications of these RE systems include quick reference design of old parts, statistical process control or quality control of parts, modification of old designs for which there no CAD data available but the some of the parts are available. As described in the following, the present invention provides a method and apparatus that meet these criteria and solves other shortcomings in the prior art.
In accordance with the present invention, a method and apparatus for reverse engineering of solid objects is provided, that is both fast and non-destructive,. More specifically, an original part, having a known refractive index (RI), made of a clear material is moved through a liquid interface formed by an immersion liquid having substantially the same RI of the part and a masking liquid having a different RI of the part thereby allowing an imaging system to view segments of the original part at the immersion/masking liquid interface.
In accordance with further aspects of the invention, a new method and apparatus is provided to create three-dimensional electronic representations of a solid object in a non-destructive manner for display on a computer monitor, for printing on paper, or for other desired uses. The part to be re-engineered is at least partially immersed in the immersion liquid having substantially the same refractive index as the part itself Accordingly, the immersed portion of the part would become essentially xe2x80x9cinvisible.xe2x80x9d The masking liquid having a density less than that of the immersion liquid and having a different refractive index, is maintained above the surface of the immersion liquid. The at least partially immersed part is then viewed through a CCD camera linked to a digital signal processor. In this manner, the cross-sectional image of the part, as it appears at the liquid interface between the immersion liquid and the lower density masking liquid, is relayed to the digital signal processor. This relaying of information may be continuous or step-wise as the part is moved upward (or downward) through the immersion/masking liquid interface to provide a complete or partial record of its cross section at various surfaces of interest. The raising or lowering of the part may be carried out by a Z-axis linear slide/stepper motor and controller with a predetermined step size.
Image acquiring at the immersion liquid-low density liquid interface, of the cross-sectional images of the immersed part, is carried out by an apparatus for acquiring data such as a CCD camera in a continuous or step-wise mode. The data processing for the captured images can then be performed using relevant software and the software will allow images to be stored in any desired image format. Images are then processed to xe2x80x9ctwo color imagesxe2x80x9d using, for example, Paintshop Pro(trademark) software or its equivalent. This step allows the method to perform the step of image edge detection. Image detection is in turn carried out using, for example, Paintshop Pro(trademark) software or its equivalent. The images are then converted using a raster-to-vector software, supplied by KVEC. This software then permits export of the cross-sectional information as DXF files. Another type of software, such as CADKEY 97(trademark) or its equivalent, may be used as a CAD program to import the DXF files and expand them into three dimensions to create three-dimensional electronic representation of a solid object. This same software can also be used to edit or manipulate any cross sections or surfaces, if necessary.
The invention also contemplates combining all of the above-mentioned software into a single program for carrying out all of the functions as described. In addition, the software may also control the Z-position of the part by controlling the stepper motor through a parallel port of a digital signal processor.
Once a complete digital image of the part has been formed, the information stored in the digital signal processor may then be used to prepare a solid prototype, which is a copy of the original part, using any rapid prototyping machine